In the treatment of visual acuity deficiencies, correction by means of eyeglasses or contact lenses are used by a large percentage of the population. Such deficiencies include patients having hyperopia or being far-sighted, myopia or near-sighted patients as well as astigmatisms caused by asymmetry of the patient's eye and presbyopia caused by loss of accommodation by the crystalline lens. Although the use of contact lenses is widespread, there are potential difficulties in properly fitting a lens for a patient, which in turn could damage the patient's cornea or cause discomfort. More recently, to alleviate the burden of wearing eyeglasses and/or contact lenses, surgical techniques have been developed for altering the shape of the patient's cornea in an attempt to correct refractive errors of the eye. Such surgical techniques include photorefractive keratectomy (PRK), LASIK (laser in-situ keratectomy), as well as procedures such as automated lamilar keratectomy (ALK) or implanted corneal rings, implanted contact lenses, and radial keratotomy. These procedures are intended to surgically modify the curvature of the cornea to reduce or eliminate visual defects. The popularity of such techniques has increased greatly, but still carry risk in both the procedure itself as well as post surgical complications.
Alternatives to permanent surgical procedures to alter the shape of the cornea includes CRT and ortho-K, where a modified contact lens is applied to the eye to alter the shape or curvature of the cornea by compression of the corneal surface imparted by the lens. The reshaping of the cornea in orthokeratology has been practiced for many years, but typically has required a series of lenses and an extensive period of time to reshape the cornea. It is also typical of orthokeratology treatment plans that the lenses used for reshaping of the cornea must be custom designed and manufactured, thereby greatly increasing the cost and complicating general use of such procedures. Further, orthokeratology lenses typically have various deficiencies, particularly relating to properly designing a lens for a particular patient to achieve best results in the treatment process. Specifically corneal abrasions from poorly distributed bearing, corneal warpage from decentered lenses, edema from tight fitting lenses and discomfort from excessive lens edge standoff are problems associated with an improperly fit lens. The design of orthokeratology lenses have not lent themselves to be easily fitted for a particular patient and their needs, requiring a doctor or other practitioner to have significant skill in complex geometric computation to properly mate the lens shape to the patients cornea and a high level of expertise in properly fitting a patient. Further, even with a high level of expertise, a lens designer many times will design a lens which will not work properly with a patient, and must be redesigned to account for the errors of the original design. Such a process is lengthy and increases the cost of the treatment correspondingly. It would be desirable to provide a lens for corneal refractive therapy which would allow a novice fitter to more easily select and arrive at a final design to simplify the fitting process.
Another deficiency of ortho-K lenses is found in the complexity of the designs, which exacerbate the fitting problems mentioned previously. In the fitting process, if there is an aspect of the lens design which is not properly fitted for the desired treatment of the patients eye, or causes excessive discomfort to the patient, the lens must be redesigned accordingly. Unfortunately, in an attempt to redesign a lens, a practitioner may affect other aspects of the lens due to the interdependency between design features or may not anticipate manufacturing variances required by the altered design. It would be worthwhile to provide a CRT lens having independent features, which could be easily modified if required to attain a proper fit in a simpler and more cost-effective process. It would also be desirable to provide an CRT lens design which enhances the ability of a fitter and a consultant to discuss more clearly the lens cornea relationship, to enable parameters of the lens to be easily communicated to a finishing laboratory for forming a desired lens.